Printed wiring board

Abstract

The present invention relates to a printed wiring board, and more particularly to a solder resist film applied on the printed wiring board, and to solder resist printing ink utilized to form such solder resist film.

We claim: 
     
       1. A printed wiring board comprising: a base plate composed of electrically insulative material and having opposed major surfaces; a conductor pattern printed on at least one major surface of the base plate; and a foamed solder resist film formed on the one major surface of the base plate at least in the region of the conductor pattern, the foamed solder resist film covering the exposed areas of the base plate surface which surround the conductors of the conductor pattern and being composed of a thermally decomposed foamed material. 
     
     
       2. A printed wiring board according to claim 1 ; wherein the foamed solder resist film has a thickness more than twice that which existed before thermal decomposition of the thermally decomposed foamed material. 
     
     
       3. A printed wiring board according to claim 2; wherein the thermally decomposed foamed material comprises material heat-treated to about 100° to 200° C. 
     
     
       4. A printed wiring board according to claim 2; wherein the foamed solder resist film comprises a solder resist film-forming ink having mixed therein a thermally decomposable foamable agent. 
     
     
       5. A printed wiring board according to claim 4; wherein the foamable agent is present in an amount equal to 2 to 5 weight percent of the solder resist film-forming ink. 
     
     
       6. A printed wiring board according to claim 4; wherein the solder resist film-forming ink contains a foam control agent. 
     
     
       7. A printed wiring board according to claim 6, wherein the foam control agent comprises dimethyl-thyrozixe. 
     
     
       8. A printed wiring board according to claim 1; wherein the thermally decomposed foamed material comprises material heat-treated to about 100° to 200° C. 
     
     
       9. A printed wiring board according to claim 1; wherein the foamed solder resist film comprises a solder resist film-forming ink having mixed therein a thermally decomposable foamable agent. 
     
     
       10. A printed wiring board according to claim 9; wherein the foamable agent is present in an amount equal to 2 to 5 weight percent of the solder resist film-forming ink. 
     
     
       11. A printed wiring board according to claim 9; wherein the solder resist film-forming ink contains a foam control agent. 
     
     
       12. A printed wiring board according to claim 11; wherein the foam control agent comprises dimethyl-thyrozixe.